ViewSonic VX715 power issues

Don_HH2K · 06-29-2009, 06:14 PM

On my way home a few days ago I found a ViewSonic VX715 LCD monitor out on the road, so naturally I took it home. On the first try it powered on, displayed "No Signal", and immediately turned off. I tried it with an old laptop connected via VGA and was able to get video off it for about a second, until it turned off again.

There had been some rain earlier that day, so I opened it up and cleared it out with a hairdryer. After this it worked for about four hours, then shut off and resumed the on/off pattern mentioned above. Subsequent attempts with the hairdryer produced the same results.

By applying the hairdryer for about 30 sec to various parts of the board, I traced the problem to the area around the two inverter transformers (part no. 80LL15T). If I unplug one but not both, the screen will stay turned on for about five seconds, then the backlight dies but the screen stays on - I can see what's on the panel itself if I angle a flashlight at it properly. If I leave both plugged in, power will cut to everything, including the panel and the status LED, within one second of turning it on. Leaving both unplugged operates as expected but isn't particularly useful for obvious reasons.

So this has led me to believe that the power supply is, for whatever reason, unable to feed the backlight starters. Since heating with the hairdryer preheats the tubes, they'd be able to flash right on without the starter. But I can't explain why they would kick out after some period of time has elapsed. Has anybody got any ideas?

06-29-2009, 06:14 PM	#1 (permalink)
Don_HH2K Registered User Join Date: Jun 2009 Posts: 1 OS: Debian GNU/Linux 5	ViewSonic VX715 power issues On my way home a few days ago I found a ViewSonic VX715 LCD monitor out on the road, so naturally I took it home. On the first try it powered on, displayed "No Signal", and immediately turned off. I tried it with an old laptop connected via VGA and was able to get video off it for about a second, until it turned off again. There had been some rain earlier that day, so I opened it up and cleared it out with a hairdryer. After this it worked for about four hours, then shut off and resumed the on/off pattern mentioned above. Subsequent attempts with the hairdryer produced the same results. By applying the hairdryer for about 30 sec to various parts of the board, I traced the problem to the area around the two inverter transformers (part no. 80LL15T). If I unplug one but not both, the screen will stay turned on for about five seconds, then the backlight dies but the screen stays on - I can see what's on the panel itself if I angle a flashlight at it properly. If I leave both plugged in, power will cut to everything, including the panel and the status LED, within one second of turning it on. Leaving both unplugged operates as expected but isn't particularly useful for obvious reasons. So this has led me to believe that the power supply is, for whatever reason, unable to feed the backlight starters. Since heating with the hairdryer preheats the tubes, they'd be able to flash right on without the starter. But I can't explain why they would kick out after some period of time has elapsed. Has anybody got any ideas?